MARINE DEPOSITS 199 



calcium carbonate in the deposits by chemical 

 analysis, and to indicate the nature of the 

 organisms which yield this ; the residue 

 after the removal of the lime by weak acid is 

 then subjected to microscopic analysis. The 

 following is a sample description : — 



S.S. " Britannia," Sounding No. 75. — ^May 23, 1899, 

 Zr 37' N., 35° 23' W., 2330 fathoms. 

 Globigerina Ooze, light brown or fawn colour, coherent, 

 granular. 

 Calcium Carbonate (62-5 per cent.), principally 

 made up of shells of pelagic foraminifera (including 

 Orhulina universa, Globigerina inflata, bulloides, 

 cequilateralis, rubra, conglobatay Pulvinulina miche- 

 liniana, canariensis, menardii), with a few bottom- 

 living foraminifera, echinid spines, ostracods, 

 coccoliths, rhabdoliths, a few coccospheres. 

 Residue (37-5 per cent.), brown: 



Minerals (5 per cent.), mean diam. 0-1 mm., angular, 



pumice, volcanic glass, felspar, etc. 

 Siliceous organisms (2 per cent.), sponge spicules, 



radio] aria, arenaceous foraminifera. 

 Fine washings (30-5 per cent.), amorphous clayey 

 matter, and minute mineral and siliceous particles. 



The " fine washings " consist largely of 

 hydrated decomposition-products of the type 

 of clay, but include also varying proportions 

 of very finely-divided undecomposed minerals, 

 which cannot be separated from the clay 

 except by chemical means. 



From the point of view of their origin, 

 marine deposits may be divided into two 

 great classes : terrigenous and pelagic. 



